Showing papers on "Lanthanum published in 1989"

Optical study of the metal-insulator transition on Ba 1–x K x Bi0 3 thin films

Abstract: THE superconducting perovskite (Ba, K)BiO3 (refs 1, 2) has the highest transition temperature known (Tc≈css31 K) aside from the copper oxide compounds3. This system becomes superconducting upon the substitution of monovalent potassium for divalent barium in the parent insulator BaBiO3, analogous to the substitution of strontium for lanthanum in La2CuO4. To understand whether the mechanism of the superconductivity is the same as in the copper oxide compounds, it is important to know the origin of the insulating state of the parent material, as well as the basic character of the metallic state induced by the cation substitution. In the case of its predecessor Ba(Bi,Pb)O3, optical measurements were used to investigate the change in electronic state across the metal-insulator transition at 65% lead doping4. Here we report the successful synthesis of (Ba,K)BiO3 thin films, which has allowed us to measure the optical spectrum, as well as the transport coefficients of (Ba,K)BiO3. Our results, combined with the previous report of the X-ray crystal structure5, strongly suggest that the Peierls gap, responsible for the insulating state of BaBiO3, almost completely vanishes at the metal-insulator transition, resulting in a metallic state described by band theory6.

Ceramic solid electrolyte-based electrochemical oxygen concentrator cell

Abstract: The invention is a ceramic solid electrolyte based electrochemical oxygen concentrator cell and the method for fabricating said cell. The cell is based on a doped cerium oxide ceramic solid electrolyte and lanthanum strontium cobaltite ceramic electrodes.

A lanthanum containing catalyst for treating automotive exhaust gas.

Abstract: This invention relates to an improved catalytic composite for treating an exhaust gas comprising a first support which is a refractory inorganic oxide, having dispersed thereon at least one oxygen storage component and at least one noble metal component and having dispersed immediately thereon an overlayer comprising lanthanum oxide and optionally a second support which is a refractory inorganic oxide. The first and second support may be selected from the group consisting of alumina, silica, titania, zirconia and aluminosilicates with alumina being preferred. Additionally, the noble metal component may be selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium. The oxygen storage component is an oxide of a metal which includes cerium, iron, nickel, cobalt lanthanum, neodymium, praesodymium, etc. and mixtures thereof. This invention also relates to a process for treating automotive exhaust comprising contacting the exhaust with the catalytic composite described above. The catalytic composite shows improved activity, especially for eliminating NOx, after extensive durability testing and also minimizes the formation of H2S.

An EXAFS structural approach of the lanthanum-gallium-sulfur glasses

Abstract: Three La: Ga:S glassy compositions spanning the range of the vitreous region, have been investigated by EXAFS (gallium K-edge, lanthanum LIII edge). As a first result, the gallium is found tetracoordinated for any composition and the GaS4 polyhedra are the glassy former units (average GaS distances = 2.27 A ). The lanthanum modifying cation has the same mean surrounding as in the crystalline state, but with more dispersed LaS distances (average LaS surrounding = seven first neighbours, situated from 2.91 to 2.93 A). However disordered, this environment is well defined. A structural model is then proposed as a covalent network of GaS4 tetrahedra, intercalated by the essentially ionic LaS channels. This model is close to the modified random network usually presented for the oxide glasses.

Catalysts for the oxidative conversion of methane to higher hydrocarbons

Abstract: An oxidative coupling catalyst composition for converting methane to a higher hydrocarbon comprising a mixed oxide of: a) a Group IIIB metal selected from the group consisting of yttrium, scandium and lanthanum; b) a Group IIA metal selected from the group consisting of barium, calcium and strontium; and c) a Group IVA metal selected from the group consisting of tin, lead and germanium and wherein the cationic species are present in the approximate ratio of 1:0.5-3:2-4, respectively, and an improved process employing same.

Infrared study of low-temperature carbon monoxide adsorption on lanthanum sesquioxide

Abstract: Etude de la chimisorption a 100°K, 140°K et 300°K sur La 2 O 3 modifie par un traitement thermique (500°-1200°K)

An X-Ray investigation of the phase relationships in the system LaH2LaH3

Abstract: The lattice constants of 24 LaH x samples in the hydrogen concentration range 1.93 ⩽ x ⩽ 2.90 were measured in the temperature range 110–140 K. Three different composition ranges of a cubic-to-tetragonal distortion were found. The low temperature subsolidus phase diagram of the lanthanum sublattice was constructed based on the X-ray measurements. The structure of the lanthanum trihydride is possibly non-cubic or has a phase transition to a non-cubic modification.

Solid compositions for fuel cell electrolytes

Abstract: A solid O2- conducting material for use as an electrolyte (152) for a fuel cell, comprising: a monocrystal or polycrystal structure of the formula: A1-xBxZ, wherein, A is independently selected from lanthanum, cerium, neodymium, praseodymium, scandium or mixtures thereof; B is independently selected form strontium, calcium, barium or magnesium; x is between about 0 and 0.9999; Z is selected from the group consisting of F3-x and OcFd where F is fluorine, O is oxygen, x is between about 0 and 0.9999 and 2c+d = 3-x, wherein c is between 0.0001 and 1.5 and d is between 0.0001 and less than or equal to 3, with the proviso when A is lanthanum, Z is F3-x and x is 0, the solid material is only a monocrystal. Composite fuel cell of thin lanthanum strontium fluoride having a laminate (composite)-type structure (151, 152, 153, 154). In another aspect, the solid electrolyte for a fuel cell is a monocrystal or polycrystal structure of PbeSnfFg, where Pb is lead and Sn is tin. The use of the solid electrolyte fuel cells disclosed to generate electricity.

Low temperature synthesis of cubic lanthanum sulfide (La2S3) powders

Abstract: Sulfide compounds are currently being developed as optical window materials for the visible and the 8–14 μm IR bands. While research in the development of ZnS and CaLa 2 S 4 materials has matured to an extent, the potential of cubic La 2 S 3 as an optical material for the far-IR window technology remains relatively unexplored. We report a wet chemical synthesis route for the preparation of lanthanum oxysulfide precursors from metal alkoxides. Using X-ray diffraction and scanning electron microscopy to characterize the phase development and morphology of the as-prepared and transformed powders, the oxysulfide precursor has been shown to transform into the cubic (γ) form of La 2 S 3 .

The separation of neodymium by quaternary amine from didymium nitrate solution

Abstract: The extraction of neodymium from didymium nitrate solution (a mixture of 83% Nd, 15% Pr and 2% other rare earths) by quaternary amine (Aliquat 336) was studied in a 45-stage tube-type mixer-settler. Six different banks in the system were used for solvent pretreatment, neodymium-stripping, feed-loading, neodymium-loading, NdPr partition and protactinium-stripping. The organic phase containing 0.6 M Aliquat 336 was equilibrated with NH4NO3 solution before entering the neodymium-loading bank, then partially fed to NdPr partition bank after extracting neodymium ions from aqueous solution, which contained diethylenetriamine pentaacetic acid as chelating agent. The other part of organic phase loaded with neodymium ions was stripped with dilute HNO3, and 95% of the neodymium with high purity (>99%) was recovered. In the praseodymium stripping bank, about 80% protactinium mixed with cerium, lanthanum and neodymium was obtained in aqueous solution.

Mixed-solid solution tri-metallic oxide/sulfide catalyst and process for its preparation

Abstract: A mixed-solid solution tri-metallic oxide/sulfide catalyst having the formula: M.sub.I O.sub.a S.sub.b.M.sub.II O.sub.c M.sub.III O.sub.d wherein M I is vanadium, neodymium, tantalum, chromium, molybdenum, tungsten, and mixtures thereof; O is oxygen; S is sulfur; a is selected from zero and a number up to a positive real number representing the stoichiometric requirement, and b is selected from zero and a number up to a positive real number representing the stoichiometric requirement, provided one of a and b is a positive real number; M II is titanium, zirconium, hafnium, and mixtures thereof; c is a positive real number up to the stoichiometric requirement; M III is lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, zinc, cadmium, mercury, scandium, yttrium, lanthanum, actinium, and mixtures thereof; and d is a positive real number up to the stoichiometric requirement; and wherein M I O a S b is mixed in a solid solution of M II O c M III O d . A process for production of the above catalyst and its use in hydroforming reactions is taught.

A hydrogen-1, chlorine-35, and lanthanum-139 NMR coordination study of the lanthanum (III) ion in aqueous solvent mixtures

Abstract: A La(III) hydration study has been carried out for solutions of La(ClO4)3 and, in a preliminary way, La(NO3)3 in aqueous mixtures with acetone-d6 and Freon-12, using hydrogen-1, chlorine-35, and lanthanum-139 NMR spectroscopy. Low temperature, proton magnetic resonance experiments allowed the direct observation and area evaluation of separate signals for water molecules in the primary solvation shell of La(III) and in bulk medium. Measurements over a wide range of salt and solvent concentration gave a maximum La(III) hydration number of 6 and no evidence for inner-shell ion-pairing in La(ClO4)3 solutions. Chlorine-35 chemical shift and linewidth data in these solutions confirmed the absence of contact ionpairing. Hydration numbers of 3–4 for La(III) in several La(NO3)3 solutions clearly indicated inner-shell complex formation. Lanthanum-139 chemical shift and linewidth measurements for these systems revealed the presence of some process, possibly hydrolysis, in the La(ClO4)3 solutions at extremely high acetone-d6 concentrations.

Synthesis of air-sinterable lanthanum chromite powders

Abstract: Lanthanum chromites, used as current interconnections in solid oxide fuel cells (SOFCs), have high electrical conductivity and are chemically stable. However, they are difficult to fabricate under conditions compatible with other SOFC components. A novel powder synthesis technique, the glycine/nitrate process, has been developed that produces chromite powders that can be sintered to near-full density in air at 1823 K. This paper describes the glycine/nitrate process for the synthesis and fabrication of lanthanum chromites. The sintering behavior and properties of a series of glycine/nitrate-produced lanthanum chromites are discussed. Some of the materials produced by this method match the thermal expansion of the electrolyte and maintain high electrical conductivity. 16 refs., 10 figs.

Preparation and properties of uniform mixed colloidal particles; VI, copper(II)–yttrium(III), and copper(II)–lanthanum(III) compounds

Abstract: Uniform spherical colloidal particles of mixed internal composition were obtained by aging at 90 °C solutions containing Cu(NO3)2 + Y(NO3)3 and Cu(NO3)2 + La(NO3)3, respectively, in the presence of urea. The molar ratio of metal ions in the solids precipitated from a given solution varied with the reaction time. After sufficiently long aging, this ratio corresponded closely to that in solutions in which the particles were generated. The original precipitates consisted of basic carbonates, which on calcination converted to mixed oxides of defined composition.

Surface treatment of metals

Abstract: Metal surfaces are heated with an aqueous treatment medium which is a solution of yttrium and metal of the lanthanum series or a suspension of particles of alumina with bound chromate followed by treatment with a solution of organosilane. Bonding of adhesives or surface coatings is improved.

The influence of certain reactive elements on the oxidation behaviour of chromia- and alumina-forming alloys

Abstract: The influence of implanted yttrium and lanthanum on the oxidation behaviour of Co25Cr1Al chromia former as well as of β-NiAl alumina former has been studied under isothermal and thermal cycling conditions in the temperature range 1273–1573 K. It has been found that protective properties of Cr 2 O 3 scale and its adherence to the substrate are greatly improved by both reactive element additions. This beneficial effect results, on the one hand, from promotion of fine-grained scale formation and on the other, from changing the mechanism of scale growth from the outward diffusion of cations to the inward diffusion of anions. The influence of implanted yttrium (but not lanthanum) on the growth mechanism and adherence of alumina scale is analogous: the scale adherence is greatly improved but its growth rate is only slightly reduced. Lanthanum, on the other hand, greatly improves the protective properties of the scale but does not, in practice, affect its adherence to the substrate. As in the case of chromia formers, it has been found that the presence of reactive element atoms in the surface layer of the substrate considerably influences the mechanism of alumina scale growth by changing it from predominant inward diffusion of anions to prevailing outward diffusion of cations. It is believed that the influence of an implanted reactive element on the oxidation behaviour of both chromia and alumina formers consists mainly in changing the mechanism of scale growth and in various interfacial phenomena.